T-SQL Script: Run The Same SQL Command Against All SQL Server Databases

Example from this webpage:

--This query will return a listing of all tables in all databases on a SQL instance:
DECLARE @command varchar(1000)
SELECT @command = 'USE ? SELECT name FROM sysobjects WHERE xtype = ''U'' ORDER BY name'
EXEC sp_MSforeachdb @command

What about the "?" Placeholder
Throughout the examples provided above you'll see the use of the question mark as a placeholder for the database/database name. To reference the database name as a string to be returned in a query, embed it between a double set of single quotation marks. To treat it as a reference to the database object simply use it by itself (as presented in Example 3b.) It is necessary to set the database for the query to run against, by using the USE ? statement, otherwise the code will execute in the context of the current database, for each database in your SQL instance. If you have 5 databases hosted in the current instance and you were to run the stored procedure code above while in the context of DBx it would execute the T-SQL text of the @command 5 times in DBx.

Summary
sp_MSforeachdb is extremely useful for pulling together metadata about your various SQL databases. I use it quite frequently for reporting on such important metrics as database file sizes, amount of free space, and backup status.